NEW YORK - Everybody knew he rode his bike through the streets of Manhattan, played softball and Frisbee in Central Park, and made grand entrances at black-tie galas.
But John F. Kennedy Jr. also worked - quietly but very intensively, his associates say - with several charity groups that have donated millions of dollars and helped thousands of people in the city he made his own.
In 1988, the year People magazine declared him ''the sexiest man alive,'' Kennedy formed Reaching Up, an organization to improve care for the mentally handicapped.
Three years later, he joined the board of the Robin Hood Foundation, a group started by Wall Street millionaires that gives more than $1 million a month to programs to help the city's impoverished children.
''This was no resume-builder for him,'' Peter Kiernan III, Robin Hood's chairman, as well as a managing director at the Goldman Sachs investment house, said yesterday. ''This was not a subtle, slight involvement. He was very engaged. He was a full partner. Quite often, he kept us focused on our mission when we started to drift away.''
For some of the group's causes, including a school in Harlem, Kennedy was the one who initiated the contact and encouraged the board to act.
''He came to every board meeting, went to look at every place we invested in,'' Kiernan said. ''When we went to a school, he'd talk with the strategic-planning people, and John was very good at that. But he'd also plunge right in there with the schoolchildren. `Hey, kids, what's going on.' He'd get into conversations with them. ... We lost a great guy here.''
Reaching Up grew out of the Kennedy family's longstanding charity work with the mentally retarded, which began as a tribute to his father's sister, Rosemary, who has been institutionalized for many years.
''John spent about a year investigating how to get involved in this,'' said Bill Ebenstein, the executive director of Reaching Up. ''And he realized the best way to support people with disabilities was to support the workers who provided services for them, by creating a program for them in higher education and helping them pay for it.''
Barbara Anselm, now the director of an adult day care program for United Cerebal Palsy in Brooklyn, was a caseworker and advocate for the handicapped in 1991, when Kennedy awarded her a stipend, one of the first.
''It helped me pay the tuition so I could go to classes at night,'' Anselm recalled. ''I met John Kennedy. He told me he had selected my application himself. It was nice to know - it encouraged me to know - that people of that stature were supporting me.''
Before Reaching Up, Ebenstein said, people like Anselm had few professional prospects.
''These were people with low-wage jobs, poverty jobs really,'' he said. ''There was no career ladder. Politicians were talking then about `quality health care,' but John realized you could never build a quality system of services unless you had quality jobs for the front-line workers.''
So, Kennedy funded - and persuaded professionals in a variety of fields to develop - a series of courses on disabilities at the City University of New York, especially its East Side Manhattan branch at Hunter College.
''He'd bring public and private entities together to work out how to do this: city and state agencies, the public universities, the hospital workers' unions,'' Ebenstein said. ''He could hold a coalition like this together. He led these meetings, visited all the places, knew all the executive directors.''
Ebenstein is unsure whether the organization can continue without Kennedy. ''Keeping these entities together - you've got all this infighting and politics - you need someone who can transcend that,'' he said. ''I'm hoping we can keep doing it, but I don't know.''
In the decade since it began, Reaching Up has awarded stipends to 400 Kennedy Fellows, 90 percent of whom have stayed in the field of helping the disabled. Ebenstein estimated that an additional 1,000 students have taken college courses that the organization has created.
Kennedy played down his involvement in these areas.
David Saltzman, who is executive director of the Robin Hood Foundation and went to Brown University with Kennedy in the 1980s, declined to talk specifically about his role in the organization.
''He was a friend of mine,'' Saltzman said. ''He asked me to respect his privacy, and I'm going to continue doing that.''
Ebenstein made the same point: ''He did not seek publicity. We'd win an award, and I'd say, `Can't we put out a news release?' He'd say, `No.' He feared people would just focus on him and miss the substance of what he was doing.''